1. Field of the Invention
The invention relates to an AC LED device and, in particular, to a continuous dimming AC LED device.
2. Description of Related Art
The conventional illumination device usually installs a dimmer at the power supply end of a light bulb to control the conduction angle of a thyristor in the dimmer under an AC sinusoidal wave. This in turn controls the sinusoidal voltage passing through the light bulb, thereby making a continuous change in the brightness of the bulb. In other words, the sinusoidal wave voltage to the light bulb is larger when the conduction angle of the thyristor is larger than when the conduction angle is small. Thus, the light bulb is brighter in the former case. To reduce the brightness of the bulb, one reduces the thyristor conduction angle, providing a lower sinusoidal wave voltage to the bulb, so that its brightness is decreased.
If the dimmer is used on an LED bulb, wherein the LED bulb is formed by multiple LEDs connected in series or in parallel, a controller is used to adjust the brightness of the LED bulb. When the supply voltage of the dimmer is lower than the required working voltage of the controller, the controller fails to function so that the LED bulb turns off immediately. This is because the controller needs a constant working voltage to function and dim light. This makes the dimmer lose the effect of gradually dimming light. When the LED light bulb is equipped with the dimmer, the dimming range thereof is limited.